Inkjet printing is a conventional technique by which printing is accomplished without contact between the printhead and the medium or substrate on which the desired print characters are deposited. Such printing is accomplished by ejecting ink from an inkjet printhead of a printing apparatus via numerous methods which employ, for example, pressurized nozzles, electrostatic fields, piezo-electric elements and/or heaters for vapor phase droplet formation.
One feature of a hand-held printer is the random motion printing as to compared to a conventional linear-type printer. Most digital printers operate by moving paper under the printing element. This is true for “page printers” which have an active print zone extending across the full width of the paper and true for “serial printers” that also move the print element across the page width in addition to moving the length of the paper by the printing element. This relative movement of paper and print element is the traditional configuration for digital printers. An alternative approach is to fix the position of the paper while the print element is moved over the paper during printing. An example of this alternative approach is a flat bed plotter where the movement of the print element is controlled by fixed mechanical references along and outside the paper edges. The present invention utilizes a printer which is moved manually over the surface of the paper without mechanical linkage and without mechanical control from a fixed reference point. This category of printer is sometimes called a “hand printer” or “random motion printer.” One advantage of this category of printer is the potential for compact size which makes it attractive for mobile printing operations.
Because of the effect on resolving print quality, a significant factor in printer design is the accuracy of positioning the print element relative to the paper during the printing process. To increase accuracy, position sensors are often adopted to “close the loop” and confirm location. Such sensors typically detect rotation of paper feed rolls or lateral travel of the carrier for the print element. Without precise sensing, small errors can accumulate until the print quality becomes unacceptable.
In a conventional linear printer, an array of optical sensors are typically utilized to detect movement, printed regions, media type and paper state. However, typical hand-held printers do not include such an array of optical sensors due to size, costs and other technological barriers. In order for the hand-held inkjet printer to be easy to use, the hand-held printer has space limitations and minimal complexity in design. For example, the hand-held printer may include only one or two optical sensors typically utilized for location determination. As such, there is a need for new methods of improving print quality with a hand-held inkjet printer. Accordingly, improved methods of printing are desired.